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To use this content you should do your own independent analysis to determine whether or not your use will be Fair. Cells and Tissues Sequence Medical Histology Epithelium Fall, 2008 Tissues [ Fr. Tissu, woven ; L. texo, to weave ] A tissue is an organized aggregation of cells or groups of cells that function in a coordinated manner to perform one or more specific functions. Tissues combine to form larger functional units, called ORGANS. Thus, the tissues are the basic functional units responsible for maintaining body functions. BASIC TISSUES Epithelium Connective tissue Muscle Nervous tissue Blood Epithelium is a cohesive sheet of cells that: 1. Covers the external surface and lines the internal surface of the body. – Protection (by withstanding wear and tear, from hydration and dehydration) – Transport (i.e. O2 and C02) – Selective Absorption: (Control the movement of substances between the outside environment and the internal compartments in the body.) – Secretion (secretory cells) 2. Forms endocrine and exocrine secretory glands. duct Secretory portion Junquueira & Carneiro 10th Ed. P. 82 Junqueira and Carnein 10th Ed. P. 82 Epithelial lining cells of Skin Intestine Michigan Medical School Histology Slide Collection Michigan Medical School Histology Slide Collection Multiple layers of flat (squamous) cells Single layer of tall (columnar) cells Epithelial cells: 1. Form avascular sheets that differ in number of cell layers, shape of the cells and structural specializations of the free (apical) cell surface, depending on the tissue function(s). 2. Are structurally and functionally polarized: Have apical, lateral and basal domains. 3. Are held together by several specializations, known as the intercellular junctions, and bind to the underlying connective tissue via the basement membrane (LM) or basal lamina (EM). 4. Are capable of renewal and regeneration. non-specialized epithelium - all cells specialized epithelium - stem cells Ross/Romrell p. 52 Epithelial cells: 1. Form avascular sheets that differ in number of cell layers, shape of the cells and structural specializations of the free (apical) cell surface, depending on the tissue function(s). 2. Are structurally and functionally polarized: Have apical, lateral and basal domains. 3. Are held together by several specializations, known as the intercellular junctions, and bind to the underlying connective tissue via the basement membrane (LM) or basal lamina (EM). 4. Are capable of renewal and regeneration. non-specialized epithelium - all cells specialized epithelium - stem cells Ross/Romrell p. 52 Classification of Epithelium (Pseudostratified) columnar (Respiratory) Ross/Romrell p. 53 Pseudostratified Epithelium Kierszenbaum p.6 Simple squamous epithelium: endothelium and mesothelium Michigan Medical School Histology Slide School Kierszenbaum p.4 Endothelium/Mesothelium (Simple Squamous Epithelium) Source Undetermined Simple Cuboidal Epithelium Michigan Medical School Histology Slide School Kierszenbaum p.4 Simple Columnar Epithelium Source Undetermined Michigan Medical School Histology Slide School Kierszenbaum p.4 Simple columnar epithelium lining the gut lumen lumen Two layers of smooth muscle on Gray’s Anatomy, wikimedia commons the wall Michigan Medical School Histology Slide School Apical Cell Surface Specializations - 1 Striated Border (Microvilli) G G Sources Undetermined G: goblet cell Microvilli (Core of actin filaments) Darnell et al., Molecular Cell Biology p. 608 Source Undetermined Apical Cell Surface Specializations – 2 Cilia on the Respiratory Epithelial Cells Verhey. Molecular Biology of the Cell, 4th Edition. Kierszenbaum p.6 Cilia core of microtubules in 9+2 arrangement (axoneme) cilia Goblet cells Basal bodies Respiratory epithelium Michigan Medical School Histology Slide Collection Source Undetermined 9 + 2 (Axoneme) Ross Dynein is responsible for the sliding. Ross et al., 4th ed. P. 94 Alberts et. Al; p 648 Dynein Defects in Immotile Cilia Source Undetermined Microvilli Microvilli and cilia Cilia Sources Undetermined Stratified Squamous Epithelium non-keratinized keratinized Kierszenbaum pg 5 Kierszenbaum pg 5 Stratified Squamous Epithelium Non-keratinized Keratinized Michigan Medical School Histology Slide Collection Michigan Medical School Histology Slide Collection Lines esophagus, oral cavity, vagina… Lines thick and thin skin Transitional Epithelium (urothelium) Kierszenbaum pg 6 Transitional Epithelium (urothelium) Lines the urinary tract, ureter, bladder and urethra Source Undetermined Epithelial cells: 1. Form avascular sheets that differ in number of cell layers, shape of the cells and structural specializations of the free (apical) cell surface, depending on the tissue function(s). 2. Are structurally and functionally polarized: Have apical, lateral and basal domains 3. Are held together by several specializations, known as the intercellular junctions, and bind to the underlying connective tissue via the basement membrane (LM) or basal lamina (EM). 4. Are capable of renewal and regeneration. non-specialized epithelium - all cells specialized epithelium - stem cells Ross/Romrell p. 52 What structures hold the cells together and attaches the epithelium to the connective tissue? Ans. Intercellular junctions Basement membrane (basal lamina) Source Undetermined Macula adherens (desmosomes) and Intermediate Filaments Source Undetermined Macula Adherens (desmosome) Adhesion Cell 1 Cell 2 plaque (plakoglobin, desmoplakins) Tonofilaments (Keratin Intermediate Filaments) Desmocollins Intercellular Space Cell Membranes Boumphreyfr, Wikimedia Commons (adapted) Source Undetermined Desmosomes and Intermediate Filaments Desmosomes serve as: 1. Spot attachment sites for adjacent cell membranes. 2. Anchoring sites for intermediate filaments. Alberts et al., p. 802 Verhey. Molecular Biology of the Cell, Garland Science 2008 Hemidesmosomes function to anchor epithelial cells to the connective tissue via basement membrane (basal lamina). Basement membrane (basal lamina) Michigan Medical School Histology Slide Collection Source Undetermined Loss of desmosome functions cause Blistering Skin Disorders Pemphigus: Separation of epidermal cells from each other (acantholysis) caused by loss of desmosome functions. Bullous pemphigoid: Separation of epidermis from the dermis due to blistering in the basement membrane caused by loss of anchoring filaments and hemidesmosomes. Source Undetermined Intercellular Junctions Junctional Complex Sources Undetermined Zonula adherens (intermediate junction) Darnell, et. al., p.608 Lady of Hats, Wikipedia Zonula adherens Macula adherens • Intermediate junction • Desmosome • Adhering junction • Adhering junction • Cadherins • Cadherins • Linked to actin • Linked to intermediate filaments filaments • Adhesion belt • Spot adhering junction Zonula Occludens (Tight Junction) serves as a Selective Permeability Barrier Junquueira & Carneiro 10th Ed. P. 82 Source